421 email error is typically a temporary routing issue on the receiving mail server's end. These should usually be resolved automatically, and you should receive a final bounce-back message if the message completely fails.

You usually would not receive a bounce-back message for this type of error. If your message is going to be delayed more than 24 hours, then sometimes a "delivery has been delayed" soft bounce will be returned to you, to let you know that the delivery has yet to complete succesfully.

Common variations of the 421 email error

  • 421 4.2.1 : (DYN:T1) http://postmaster.info.aol.com/errors/421dynt1.html
  • 421 4.3.1 Out of disk space for temp file
  • 421 4.3.2 All server ports are busy
  • 421 4.3.2 All server ports are busy
  • 421 4.4.2 mx.aol.com Error: timeout exceeded
  • 421 #4.4.5 Too many connections from your host.
  • 421 #4.4.5 Too many connections to this host.
  • 421 4.7.0 mx.aol.com Error: too many errors
  • 421 4.7.1 : (DYN:T1) http://postmaster.info.aol.com/errors/421dynt1.html
  • 421 4.7.1 POL-T2 http://postmaster.facebook.com/response_codes?ip=74.124.194.252#pol-t Connection refused
  • 421 4.7.1 POL-T2 http://postmaster.facebook.com/response_codes?ip=74.124.194.252#pol-t Connection refused

  • 421 Downstream server error
  • 421 Fork failed
  • 421 Greylisting enabled, please try later.
  • 421 LDAP verification agent temporarily unavailable: Connection failed
  • 421 mail.RemoteDomain.com out of connection slots
  • 421 mx.aol.com Service unavailable - try again later
  • 421 <recipient@RemoteDomain.com> Service not available - too busy
  • 421 Server busy, try again later - psmtp
  • 421 service temporarily unavailable
  • 421 Temporary error (#4.3.0)
  • 421 Too many concurrent SMTP connections; please try again later.
  • 421 Unexpected failure, please try later

Resolving a 421 email error

Because errors in the 421 series don't bounceback right away they would be considered a soft bounce. To better understand soft and hard bounces, and general email bounceback errors you can read why does email bounce, bounceback, or error?

Seeing a large amount of 421 email errors in your server's mail logs could be an indication that a lot of your mail users are having difficulties getting their e-mails delivered out successfully on the first attempt.

Did you find this article helpful?

We value your feedback!

Why was this article not helpful? (Check all that apply)
The article is too difficult or too technical to follow.
There is a step or detail missing from the instructions.
The information is incorrect or out-of-date.
It does not resolve the question/problem I have.
How did you find this article?
Please tell us how we can improve our Support Center:
Email Address
Optional, but our team may contact you for more information.
Like this Article?

Post a Comment

Name:
Email Address:
Comment:
Are you a bot?
Submit

Please note: Your name and comment will be displayed, but we will not show your email address.

Write New!
Do you want to publish a tutorial to our support center?

News / Announcements

SSL Certficate Warnings
Updated 2014-04-14 11:34 am EST
Hits: 2008
Heartbleed 0-day OpenSSL security bug
Updated 2014-04-14 04:43 pm EST
Hits: 5282

Related Questions

Here are a few questions related to this article that our customers have asked:
Ooops! It looks like there are no questions about this page.
Would you like to ask a question about this page? If so, click the button below!
Ask a Question

Need more Help?

Search

Ask the Community!

Get help with your questions from our community of like-minded hosting users and InMotion Hosting Staff.

Current Customers

Chat: Click to Chat Now E-mail: support@InMotionHosting.com
Call: 888-321-HOST (4678) Ticket: Submit a Support Ticket

Not a Customer?

Get web hosting from a company that is here to help. Sign up today!